Lubricating Oil Compositions

ABSTRACT

An internal combustion engine crankcase lubricating oil composition has a phosphorus content of not greater than 0.09 mass % a metal detergent additive system comprising one or more metal salts of organic carboxylic acids, and a viscosity index improver comprising a linear diblock copolymer, one block being derived from a vinyl aromatic hydrocarbon monomer and one block being derived from a diene monomer.

This invention relates to internal combustion engine crankcaselubricating oil compositions (or lubricants), more especially tocompositions suitable for use in piston engine, especially for gasoline(spark-ignited) and diesel (compression-ignited) piston enginelubrication; and to use of additives in such compositions for reducingwear.

A crankcase lubricant is an oil used for general lubrication in aninternal combustion engine where an oil sump is situated generally belowthe crankshaft of the engine and to which circulated oil returns. It iswell-known to include additives in crankcase lubricants for severalpurposes.

There has been a need and/or requirement to reduce the level ofphosphorus in crankcase lubricants in order to improve the durability ofexhaust gas treatment catalysts. Reductions in the amount ofphosphorus-containing lubricant additives can, however, cause increasedwear in the engine.

It is also known to provide salicylate-based metal detergents asadditives in crankcase lubricants.

EP-A-1 338 643 ('643) describes crankcase lubricants that containoverbased calcium or magnesium salicylate and that have less than 50 ppmof phosphorus. '643 describes tests on an example of such a lubricant,containing calcium salicylate and having no phosphorus, to measure theaverage cam wear, which is reported to be within ILSAC GF-3 engine testlimits.

A problem in '643 is that the formulations therein may exhibit poor camand lifter wear. Cam-plus-lifter wear is one of the parameters of thesequence IIIG test, which is an API Category SM, ILSAC Category GF-4test carried out during high temperature conditions and which simulateshigh-speed service during relatively high ambient temperatureconditions.

The present invention, surprisingly, and as evidenced by the datapresented in this specification, overcomes the problem by employingformulations that contain specific viscosity index improvers.

In a first aspect, the invention provides an internal combustion enginecrankcase lubricating oil composition having a phosphorus concentration,expressed as atoms of phosphorus, of not greater than 0.09 mass %, basedon the mass of the oil composition, which composition comprises or ismade by admixing:

-   -   (A) an oil of lubricating viscosity, in a major amount;    -   (B) a metal detergent system, as an additive in a minor amount,        comprising one or more metal salts of organic carboxylic acids;        and    -   (C) a viscosity index improver comprising a linear diblock        copolymer comprising at least one block derivable primarily from        a vinyl aromatic hydrocarbon monomer and at least one block        derivable primarily from a diene monomer.

In a second aspect, the invention provides a method of lubricating acompression-ignited or spark-ignited internal combustion engine, whichmethod comprises supplying to the engine a lubricating oil compositionaccording to the first aspect of the invention.

In a third aspect, the invention provides the use of a viscosity indeximprover as defined in the first aspect of the invention, to improve thecam and lifter wear in the crankcase lubrication of an internalcombustion engine by a lubricating oil composition having a phosphorusconcentration, expressed as atoms of the phosphorus, of not greater than0.08 mass % based on the mass of the lubricating oil composition.

A lubricating oil composition according to the present invention mayhave a phosphorus content of at least greater than 0.005, preferably atleast 0.01, and not greater than 0.08 mass %, based on the mass of theoil composition.

A lubricating oil composition according to the present invention mayhave a total base number (TBN) of between 2 and 9, preferably between 4and 8.

Preferably, the lubricating oil composition of the invention is a lowviscosity oil composition, such as a multigrade oil compositionsatisfying the SAE 0W-X or SAE 5W-X characteristics where X represents,for example, any one of 20, 30 and 40.

In this specification, the following words and expressions, if and whenused, shall have the meanings ascribed below:

-   -   “active ingredient” or “(a.i.)” refers to additive material that        is not diluent or solvent;    -   “comprising” or any cognate word specifies the presence of        stated features, steps, or integers or components, but does not        preclude the presence or addition of one or more other features,        steps, integers, components or groups thereof; the expressions        “consists of” or “consists essentially of” or cognates may be        embraced within “comprises” or cognates, wherein “consists        essentially of” permits inclusion of substances not materially        affecting the characteristics of the composition to which it        applies;    -   “major amount” means in excess of 50 mass % of a composition;    -   “minor amount” means less than 50 mass % of a composition;    -   “TBN” means total base number as measured by ASTM D2896.

Furthermore in this specification:

-   -   “phosphorus content” is as measured by ASTM D5185;    -   “sulphated ash content” is as measured by ASTM D874;    -   “sulphur content” is as measured by ASTM D2622;    -   “KV100” means kinematic viscosity at 100° C. as measured by ASTM        D445.

Also, it will be understood that various components used, essential aswell as optimal and customary, may react under conditions offormulation, storage or use and that the invention also provides theproduct obtainable or obtained as a result of any such reaction.

Further, it is understood that any upper and lower quantity, range andratio limits set forth herein may be independently combined.

The features of the invention relating, where appropriate, to each andall aspects of the invention, will now be described in more detail asfollows:

Oil of Lubricating Viscosity (A)

This, sometimes referred to as the base oil or base stock, is theprimary liquid constituent of the composition into which additives andpossibly other oils are blended.

A base oil may be selected from natural (vegetable, animal or mineral)and synthetic lubricating oils and mixtures thereof. It may range inviscosity from light distillate mineral oils to heavy lubricating oilssuch as gas engine oil, mineral lubricating oil, motor vehicle oil andheavy duty diesel oil. Generally the viscosity of the oil ranges from 2to 30, especially 5 to 20, mm²s⁻¹ at 100° C.

Natural oils include animal and vegetable oils (e.g. castor and lardoil), liquid petroleum oils and hydrorefined, solvent-treated minerallubricating oils of the paraffinic, naphthenic and mixedparaffinic-naphthenic types. Oils of lubricating viscosity derived fromcoal or shale are also useful base oils.

Synthetic lubricating oils include hydrocarbon oils such as polymerizedand interpolymerized olefins (e.g. polybutylenes, polypropylenes,propylene-isobutylene copolymers, chlorinated polybutylenes,poly(1-hexenes), poly(1-octenes), poly(1-decenes)); alkylbenzenes (e.g.dodecylbenzenes, tetradecylbenzenes, dinonylbenzenes,di(2-ethylhexyl)benzenes); polyphenols (e.g. biphenyls, terphenyls,alkylated polyphenols); and alkylated diphenyl ethers and alkylateddiphenyl sulfides and derivatives, analogues and homologues thereof.

Another suitable class of synthetic lubricating oils comprises theesters of dicarboxylic acids (e.g. phthalic acid, succinic acid, alkylsuccinic acids and alkenyl succinic acids, maleic acid, azelaic acid,suberic acid, sebasic acid, fumaric acid, adipic acid, linoleic aciddimer, malonic acid, alkylmalonic acids, alkenyl malonic acids) with avariety of alcohols ( e.g. butyl alcohol, hexyl alcohol, dodecylalcohol, 2-ethylhexyl alcohol, ethylene glycol, diethylene glycolmonoether, propylene glycol). Specific examples of these esters includedibutyl adipate, di(2-ethylhexyl)sebacate, di-n-hexyl fumarate, dioctylsebacate, diisooctyl azelate, diisodecyl azelate, dioctyl phthalate,didecyl phlthalate, dieicosyl sebacate, the 2-ethylhexyl diester oflinoleic acid dimer, and the complex ester formed by reacting one moleof sebacic acid with two moles of tetraethylene glycol and two moles of2-ethylhexanoic acid.

Esters useful as synthetic oils also include those made from C₅ to C₁₂monocarboxylic acids and polyols, and polyol ethers such as neopentylglycol, trimethylolpropane, pentaerythritol, dipentaerythritol andtripentaerythritol.

Unrefined, refined and re-refined oils can be used in the compositionsof the present invention. Unrefined oils are those obtained directlyfrom a natural or synthetic source without further purificationtreatment. For example, a shale oil obtained directly from retortingoperations, a petroleum oil obtained directly from distillation or esteroil obtained directly from an esterification process and used withoutfurther treatment would be unrefined oil. Refined oils are similar tothe unrefined oils except they have been further treated in one or morepurification steps to improve one or more properties. Many suchpurification techniques, such as distillation, solvent extraction, acidor base extraction, filtration and percolation are known to thoseskilled in the art. Re-refined oils are obtained by processes similar tothose used to obtain refined oils applied to refined oils which havebeen already used in service. Such re-refined oils are also known asreclaimed or reprocessed oils and often are additionally processed bytechniques for approval of spent additive and oil breakdown products.

Other examples of base oil are gas-to-liquid (“GTL”) base oils, i.e. thebase oil may be an oil derived from Fischer-Tropsch-synthesisedhydrocarbons made from synthesis gas containing hydrogen and carbonmonoxide using a Fischer-Tropsch catalyst. These hydrocarbons typicallyrequire further processing in order to be useful as a base oil. Forexample, they may, by methods known in the art, be hydroisomerized;hydrocracked and hydroisomerized; dewaxed; or hydroisomerized anddewaxed.

Base oil may be categorised in Groups I to V according to the API EOLCS1509 definition. Base oil derived from one or more of Groups III, IV andV is preferred.

The oil of lubricating viscosity is provided in a major amount, incombination with minor amounts of the additives (B) and (C) and, ifnecessary, one or more co-additives such as described hereinafter,constituting the composition. This preparation may be accomplished byadding the additive directly to the oil or by adding it in the form of aconcentrate thereof to disperse or dissolve the additive. Additives maybe added to the oil by any method known to those skilled in the art,either prior to, contemporaneously with, or subsequent to, addition ofother additives.

The terms “oil-soluble” or “oil-dispersible”, or cognate terms, usedherein do not necessarily indicate that the compounds or additives aresoluble, dissolvable, miscible, or are capable or being suspended in theoil in all proportions. They do mean, however, that they are, forinstance, soluble or stably dispersible in oil to an extent sufficientto exert their intended effect in the environment in which the oil isemployed. Moreover, the additional incorporation of other additives mayalso permit incorporation of higher levels of a particular additive, ifdesired.

Metal Detergent System (B)

Metal detergents are additives that reduce formation of piston depositsin engines and that may have acid-neutralising properties, and the term‘detergent’ is used herein to define a material capable of providingeither or both of these functions within the lubricating oilcomposition. They are based on metal “soaps”, that is metal salts ofacidic organic compounds sometimes referred to as surfactants, and thatgenerally comprise a polar head with a long hydrophobic tail.

As stated, the metal detergent system comprises one or more metal saltsor organic carboxylic acids.

Preferably the carboxylic acids are aromatic carboxylic acids; morepreferably salts of aromatic carboxylic acids constitute all of themetal detergent systems.

The aromatic moiety of the aromatic carboxylic acids can contain heteroatoms such as nitrogen and oxygen but preferably contains only carbonand hydrogen atoms, for example six or more carbon atoms. Benzene is apreferred moiety.

The aromatic carboxylic acid may contain one or more aromatic moieties,such as one or more benzene rings, either fused or connected viaalkylene bridges.

The carboxylic moiety may be attached directly or indirectly to thearomatic moiety, preferably directly to a carbon atom on the aromaticmoiety, such as a carbon atom on a benzene ring.

More preferably, the aromatic moiety also contains a second functionalgroup such as a hydroxyl group, attached directly or indirectly to acarbon atoms on the aromatic moiety.

Preferred examples of aromatic carboxylic acids are salicylic acids suchas hydrocarbyl-substituted salicylic acids. “Hydrocarbyl” means groupscontaining substantially hydrogen and carbon atoms and bonded to theremainder of the molecule directly via a carbon atoms; they may containone or more hetero atoms provided these do not detract from theessentially hydrocarbyl nature of the group.

The salts may be complexed with other surfactants such as phenates andmay be in the form of hydroxybenzoates. Alkylphenols may be present.U.S. Pat. No. 5,808,145; EP-A-0 933 417 and EP-A-0 985 726 describeexamples of such complexes.

The metal is preferably an alkaline earth metal such as calcium andmagnesium.

Another class of useful metal salts of organic carboxylic acids aremetal salts of linear and cyclic compounds containing phenol andsalicylic acid units, sometimes referred to as “salicylic calixarenes”.Such detergents are described, for example, in EP-A-0 708 171; WO 99/0025 677; WO 02/0 072 529; and WO 03/0 018 728.

Where the aromatic carboxylic acid is salicylic acid, conveniently, eachsalicylate is alkyl-substituted for example with independent alkylgroups having from 8 to 30 carbon atoms and which may be linear,branched or cyclic. As examples of alkyl groups there may be mentionedthe following: octyl, nonyl, decyl, dodecyl, pentadecyl, octadecyl,eicosyl, docosyl, tricosyl, hexacosyl, triacontyl, dimethyicyclohexyl,ethylcyclohexyl, methylcyclohexylmethyl and cyclohexylethyl.

Preferably, substantially all of the metal detergent system is calciumsalicylate in the sense that it contains, at most, minor or adventitiousamounts of metal detergents other than the calcium salicylate. Morepreferred is a metal detergent system from which metal phenates andmetal sulfonates are substantially, or more preferably completely,absent.

Conveniently, calcium salicylate, when used, provides from 50 to 4,000preferably from 100 to 3,000, ppm by mass of atoms of calcium, based onthe mass of the lubricating oil composition.

The detergent additive(s) in the detergent system may be neutral oroverbased, preferably overbased. Conveniently, they may have a TBN inthe range of 15 or 60 to 600, preferably 100 to 450.

Viscosity Index Improvers (C)

Viscosity Index Improvers, or VI Improvers, useful in the practice ofthe present invention are linear diblock copolymers that comprise atleast one block derived primarily from a vinyl aromatic hydrocarbonmonomer, and at least one block derived primarily from a diene monomer.Useful vinyl aromatic hydrocarbon monomers include those containing from8 to 16 carbon atoms such as aryl-substituted styrenes,alkoxy-substituted styrenes, vinyl naphthalene, alkyl-substituted vinylnaphthalenes and the like. Dienes, or diolefins, contain two doublebonds, commonly located in conjugation in a 1,3 relationship. Olefinscontaining more than two double bonds, sometimes referred to aspolyenes, are also considered within the definition of “diene” as usedherein. Useful dienes include those containing from 4 to about 12 carbonatoms, preferably from 8 to 16 carbon atoms, such as 1,3-butadiene,isoprene, piperylene, methylpentadiene, phenylbutadiene,3,4-dimethyl-1,3-hexadiene, 4,5-diethyl-1,3-octadiene, with1,3-butadiene and isoprene being preferred.

Linear block copolymers useful in the practice of the present inventionmay be represented by the following general formula:A-Bwherein:

-   A is a polymeric block derived predominantly from vinyl aromatic    hydrocarbon monomer; and-   B is a polymeric block derived predominantly from conjugated diene    monomer.

Also included in the definition of “linear diblock copolymers” aretapered linear block copolymers represented by the following generalformula:A-A/B—Bwherein:

-   A is a polymeric block derived predominantly from vinyl aromatic    hydrocarbon monomer;-   B is a polymeric block derived predominantly conjugated diolefin    monomer; and-   A/B is a tapered segment derived from both vinyl aromatic    hydrocarbon monomer and conjugated diolefin monomer.

As used herein in connection with polymer block composition,“predominantly” means that the specified monomer or monomer type that isthe principle component in that polymer block is present in an amount ofat least 85% by weight of the block.

Polymers prepared with diolefins will contain ethylenic unsaturation,and such polymers are preferably hydrogenated. When the polymer ishydrogenated, the hydrogenation may be accomplished using any of thetechniques known in the prior art. For example, the hydrogenation may beaccomplished such that both ethylenic and aromatic unsaturation isconverted (saturated) using methods such as those taught, for example,in U.S. Pat. Nos. 3,113,986 and 3,700,633 or the hydrogenation may beaccomplished selectively such that a significant portion of theethylenic unsaturation is converted while little or no aromaticunsaturation is converted as taught, for example, in U.S. Pat. Nos.3,634,595; 3,670,054; 3,700,633 and Re 27,145. Any of these methods canalso be used to hydrogenate polymers containing only ethylenicunsaturation and which are free of aromatic unsaturation.

The block copolymers may include mixtures of linear polymers asdisclosed above, having different molecular weights and/or differentvinyl aromatic contents as well as mixtures of linear diblock copolymershaving different molecular weights and/or different vinyl aromaticcontents. The use of two or more different polymers may be preferred toa single polymer depending on the rheological properties the product isintended to impart when used to produce formulated engine oil.

The block copolymer may have a number average molecular weight ofbetween 200,000 and 1,500,000. A number average molecular weight ofbetween 350,000 and 900,000 is preferred. The amount of vinyl aromaticcontent of the copolymer is preferably between 5% and 40% by weight ofthe copolymer. For such copolymers, number average molecular weightsbetween 85,000 and 300,000 are acceptable.

Useful block copolymers include those prepared in bulk, suspension,solution or emulsion. As is well known, polymerization of monomers toproduce hydrocarbon polymers may be accomplished using free-radical,cationic and anionic initiators or polymerization catalysts, such astransition metal catalysts used for Ziegler-Natta and metallocene type(also referred to as “single-site”) catalysts.

Preferably, the linear diblock copolymer is at least one linear diblockcopolymer having a polystyrene block and a block derived from isoprene,butadiene, or a mixture thereof More preferably, the linear diblockcopolymer is at least one linear diblock copolymer selected fromhydrogenated styrene/butadiene diblock copolymers and hydrogenatedstyrene/isoprene diblock copolymers. Preferably, the diblock copolymerhas a Shear Stability Index value, determined in accordance with theprocedure of ASTM D6278-98 (known as the Kurt-Orban (KO) or DIN benchtest), of from 2 to 50%, more preferably from 5 to 50% (30 cycles), andthe block of the diblock copolymer derived from diene comprises from 40to 90 mass % derived from isoprene and from 10 to 60 mass % derived frombutadiene.

Optionally, VI improvers used in the practice of the invention can beprovided with nitrogen-containing functional groups that impartdispersant capabilities to the VI improver. One trend in the industryhas been to use such “multifunctional” VI improvers in lubricants toreplace some or all of the dispersant. Nitrogen-containing functionalgroups can be added to a polymeric VI improver by grafting a nitrogen-or hydroxyl- containing moiety, preferably a nitrogen-containing moiety,onto the polymeric backbone of the VI improver (functionalizing).Processes for the grafting of a nitrogen-containing moiety onto apolymer are known in the art and include, for example, contacting thepolymer and nitrogen-containing moiety in the presence of a free radicalinitiator, either neat, or in the presence of a solvent. The freeradical initiator may be generated by shearing (as in an extruder) orheating a free radical initiator precursor, such as hydrogen peroxide.

The amount of nitrogen-containing grafting monomer will depend, to someextent, on the nature of the substrate polymer and the level ofdispersancy required of the grafted polymer. To impart dispersancycharacteristics to both star and linear copolymers, the amount ofgrafted nitrogen-containing monomer is suitably between 0.4 and 2.2 wt.%, preferably from 0.5 to 1.8 wt. %, most preferably from 0.6 to 1.2 wt.%, based on the total weight of grafted polymer.

Methods for grafting nitrogen-containing monomer onto polymer backbones,and suitable nitrogen-containing grafting monomers are known anddescribed, for example, in U.S. Pat. No. 5,141,996, WO 98/13443, WO99/21902, U.S. Pat. No. 4,146,489, U.S. Pat. No. 4,292,414, and U.S.Pat. No. 4,506,056. (See also J Polymer Science, Part A: PolymerChemistry, Vol. 26, 1189-1198 (1988); J Polymer Science, PolymerLetters, Vol. 20, 481-486 (1982) and J. Polymer Science, PolymerLetters, Vol. 21, 23-30 (1983), all to Gaylord and Mehta and Degradationad Cross-linking of Ethylene-Propylene Copolymer Rubber on Reaction withMaleic Anhydride and/or Peroxides; J. Applied Polymer Science, Vol. 33,2549-2558 (1987) to Gaylord, Mehta and Mehta.

Diblock copolymer components of the present invention are available ascommercial products. Examples of commercially availablestyrene/hydrogenated isoprene linear diblock copolymers include InfineumSV140™, Infineum SV150™ and Infineum SV160™, available from Infineum USAL.P. and Infineum UK Ltd.; Lubrizol® 7318, available from The LubrizolCorporation; and Septon 1001™ and Septon 1020™, available from SeptonCompany of America (Kuraray Group). Suitable styrene/1,3-butadienehydrogenated block copolymers are sold under the tradename Glissoviscal™by BASF.

The viscosity index improver may, for example, be provided in an amountfrom 0.01 to 20, preferably 1 to 10, mass % based on the mass of thelubricating oil composition.

Other Additives

Other additives, such as the following, may also be present in thelubricating oil compositions of the present invention.

Ashless dispersants comprise an oil-soluble polymeric hydrocarbonbackbone having functional groups that are capable of associating withparticles to be dispersed. Typically, the dispersants comprise amine,alcohol, amide, or ester polar moieties attached to the polymer backboneoften via a bridging croup. The ashless dispersants may be, for example,selected from oil-soluble salts, esters, amino-esters, amides, imides,and oxazolines of long chain hydrocarbon substituted mono anddicarboxylic acids or their anhydrides; thiocarboxylate derivatives oflong chain hydrocarbons; long chain aliphatic hydrocarbons having apolyamine attached directly thereto; and Mannich condensation productsformed by condensing a long chain substituted phenol with formaldehydeand a polyalkylene polyamine.

Anti-wear agents may comprise dihydrocarbyl dithiophosphate metal saltswherein the metal may be an alkali or alkaline earth metal, or aluminum,lead, tin, molybdenum, manganese, nickel, copper, or preferably, zinc.

Dihydrocarbyl dithiophosphate metal salts may be prepared in accordancewith known techniques by first forming a dihydrocarbyl dithiophosphoricacid (DDPA), usually by reaction of one or more alcohols or a phenolwith P₂S₅ and then neutralizing the formed DDPA with a metal compound.For example, a dithiophosphoric acid may be made by reacting mixtures ofprimary and secondary alcohols. Alternatively, multiple dithiophosphoricacids can be prepared where the hydrocarbyl groups on one are entirelysecondary in character and the hydrocarbyl groups on the others areentirely primary in character. To make the metal salt, any basic orneutral metal compound could be used but the oxides, hydroxides andcarbonates are most generally employed. Commercial additives frequentlycontain an excess of metal due to the use of an excess of the basicmetal compound in the neutralization reaction.

The preferred zinc dihydrocarbyl dithiophosphates (ZDDP) are oil-solublesalts of dihydrocarbyl dithiophosphoric acids and may be represented bythe following formula:

wherein R and R′ may be the same or different hydrocarbyl radicalscontaining from 1 to 18, preferably 2 to 12, carbon atoms and includingradicals such as alkyl, alkenyl, aryl, arylalkyl, alkaryl andcycloaliphatic radicals. Particularly preferred as R and R′ groups arealkyl groups of 2 to 8 carbon atoms. Thus, the radicals may, forexample, be ethyl, n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl,amyl, n-hexyl, i-hexyl, n-octyl, decyl, dodecyl, octadecyl,2-ethylhexyl, phenyl, butylphenyl, cyclohexyl, methylcyclopentyl,propenyl, butenyl. In order to obtain oil solubility, the total numberof carbon atoms (i.e. R and R′) in the dithiophosphoric acid willgenerally be about 5 or greater. The zinc dihydrocarbyl dithiophosphatecan therefore comprise zinc dialkyl dithiophosphates.

To limit the amount of phosphorus introduced into the lubricating oilcomposition by ZDDP to no more than 0.09 mass %, the ZDDP shouldpreferably be added to the lubricating oil compositions in amounts nogreater than from about 1.1 to 1.3 mass %, based upon the total mass ofthe lubricating oil composition.

Oxidation inhibitors or antioxidants reduce the tendency of base stocksto deteriorate in service which deterioration can be evidenced by theproducts of oxidation such as sludge and varnish-like deposits on themetal surfaces and by viscosity growth. Such oxidation inhibitorsinclude hindered phenols, aromatic amines, alkaline earth metal salts ofalkylphenolthioesters having preferably C₅ to C₁₂ alkyl side chains,calcium nonylphenol sulfides, ashless oil soluble phenates andsulfurized phenates, phosphosulfurized or sulfurized hydrocarbons,phosphorus esters, metal thiocarbamates and oil-soluble copper compoundsas described in U.S. Pat. No. 4,867,890.

Friction Modifiers which include boundary lubricant additives that lowerfriction coefficient and hence improve fuel economy may be used.Examples include ester-based organic friction modifiers such as partialfatty acid esters of polyhydric alcohols, for example, glycerolmonooleate; and amine-based organic frication modifiers. Furtherexamples are additives that deposit molybdenum disulphide such asorgano-molybdenum compounds where the molybdenum is, for example, indinuclear or trinuclear form.

Rust inhibitors selected from the group consisting of nonionicpolyoxyalkylene polyols and esters thereof, polyoxyalkylene phenols, andanionic alkyl sulfonic acids may be used.

Copper and lead bearing corrosion inhibitors may be used, but aretypically not required with the formulation of the present invention.Typically such compounds are the thiadiazole polysulfides containingfrom 5 to 50 carbon atoms, their derivatives and polymers thereof.Derivatives of 1,3,4 thiadiazoles such as those described in U.S. Pat.Nos. 2,719,125; 2,719,126; and 3,087,932; are typical. Other similarmaterials are described in U.S. Pat. Nos. 3,821,236; 3,904,537;4,097,387; 4,107,059; 4,136,043; 4,188,299; and 4,193,882. Otheradditives are the thio and polythio sulfenamides of thiadiazoles such asthose described in UK Patent Specification No. 1,560,830. Benzotriazolesderivatives also fall within this class of additives. When thesecompounds are included in the lubricating composition, they arepreferably present in an amount not exceeding 0.2 mass % activeingredient.

A small amount of a demulsifying component may be used. A preferreddemulsifying component is described in EP 330,522. It is obtained byreacting an alkylene oxide with an adduct obtained by reacting abis-epoxide with a polyhydric alcohol. The demulsifier should be used ata level not exceeding 0.1 mass % active ingredient. A treat rate of0.001 to 0.05 mass % active ingredient is convenient.

Pour point depressants, otherwise known as lube oil flow improvers,lower the minimum temperature at which the fluid will flow or can bepoured. Such additives are well known. Typical of those additives whichimprove the low temperature fluidity of the fluid are C₈ to C₁₈ dialkylfumarate/vinyl acetate copolymers, polyalkylmethacrylates and the like.

Foam control can be provided by many compounds including antifoamant ofthe polysiloxane type, for example, silicone oil or polydimethylsiloxane.

Lubricating oil compositions of the present invention may optionallyalso contain VI improving materials other than Viscosity Index Improvers(C), such as ethylene-propylene, or other olefin copolymer (OCP) VIimprovers, or random or linear triblock copolymers or random star orstar block copolymers derived from vinyl aromatic hydrocarbon and diene.Such other VI improvers are well known and available commercially.Preferably, Viscosity Index Improvers (C) are the sole VI improvers usedin the lubricating oil composition.

The individual additives may be incorporated into a base stock in anyconvenient way. Thus, each of the components can be added directly tothe base stock or base oil blend by dispersing or dissolving it in thebase stock or base oil blend at the desired level of concentration. Suchblending may occur at ambient temperature or at an elevated temperature.

Preferably, all the additives except for the viscosity modifier and thepour point depressant are blended into a concentrate described herein asthe additive package, which is subsequently blended into base stock tomake the finished lubricant. The concentrate will typically beformulated to contain the additive(s) in proper amounts to provide thedesired concentration in the final formulation when the concentrate iscombined with a predetermined amount of a base lubricant.

The concentrate is preferably made in accordance with the methoddescribed in U.S. Pat. No. 4,938,880.

The final crankcase lubricating oil composition may employ from 2 to 20,preferably 4 to 18, and most preferably 5 to 17, mass % of theconcentrate or additive package with the remainder being base stock.Preferably, lubricating oil compositions of the present invention have asulphated ash concentration of not greater than 1.0 mass % and/or asulphur concentration, expressed as atoms of sulphur, of not greaterthan 0.3, more preferably not greater than 0.2, mass %.

Engines

The invention is applicable to a range of internal combustion enginessuch as compression-ignited and spark-ignited two-or four-strokereciprocating engines. Examples include engines for power-generation,locomotive and marine equipment and heavy duty on-highway trucks; heavyduty off-highway engines such as may be used for agriculture,construction and mining and engines for light duty commercial andpassenger car applications.

EXAMPLES

The invention will now be particularly described in the followingexamples which are not intended to limit the scope of the claims hereof.

Two fully-formulated 5W30 lubricating oil compositions (or lubricants)were blended by methods known in the art.

Each lubricant was formulated to have the same kinematic viscosity at100° C. and contained or possessed:

-   -   a calcium salicylate detergent additive, TBN 160, giving rise to        0.114 mass % of Ca atoms;    -   a phosphorus content of 0.05 mass %;    -   a polymer content of 0.9 mass %; and    -   identical quantities of dispersant, antiwear agent, antioxidant,        friction modifier and other additives, routinely used in        formulating lubricating oil compositions.

The two lubricants differed in that:

Lubricant 1, a lubricant of the invention, contained as a viscosityindex improver 6 mass % of an isoprene/styrene linear diblock copolymerin 130N Group I basestock with 1.9 mass % polymethacrylate LOFI. Thecopolymer, having one block derived from styrene and one block ofhydrogenated polyisoprene, had a styrene content of 35 mass % and anumber average molecular weight (measured as styrene equivalent) of130,000; and

Lubricant A, a reference lubricant, contained as a viscosity indeximprover 15 mass % of star copolymer in 130N Group I basestock. The starcopolymer had hydrogenated polyisoprene arms and an overall numberaverage molecular weight (measured as styrene equivalent) of 360,000.

Each of the two lubricants was tested for cam and lifter wear accordingto the Sequence IIIG Test. The Test utilizes a 1996 General Motors 3800cc Series 11, water-cooled, 4 cycle, V-6 gasoline engine as the testapparatus. The Sequence III G test engine is an overhead valve design(OHV) and uses a single camshaft operating both intake and exhaustvalves via pushrods and hydraulic valve lifters in a sliding-followerarrangement. Using unleaded gasoline, the engine runs a 10-minuteinitial oil-leveling procedure followed by a 15-minute slow ramp up tospeed and load conditions. The engine then operates at 125 bhp, 3,600rpm and 150° C. oil temperature for 100 hours, interrupted at 20-hourintervals for oil level checks.

At the end of the Test, the cam lobes and lifters were measured forwear. The results, expressed as average cam-plus-lifter wear in microns,were as follows, where the pass limit for the Test is a maximum of 60microns. Lubricant 1 57.2 Lubricant A 291.7

The results demonstrate that the use of a linear diblock viscosity indeximprover in Lubricant 1 gave rise to dramatically better wearperformance in an accredited engine test compared to Lubricant A.

1. An internal combustion engine crankcase lubricating oil compositionhaving a phosphorus concentration expressed as atoms of phosphorus, ofnot greater than 0.09 mass % based on the mass of the oil composition,which composition comprises or is made by admixing: (A) an oil oflubricating viscosity, in a major amount; (B) a metal detergent system,as an additive in a minor amount, comprising one or more metal salts oforganic carboxylic acids; and (C) a viscosity index improver comprisinga linear diblock copolymer comprising at least one block derivedprimarily from a vinyl aromatic hydrocarbon monomer and at least oneblock derived primarily from a diene monomer.
 2. An oil composition asclaimed in claim 1 wherein the linear diblock copolymer is at least onediblock copolymer comprising at least a polystyrene block and a blockderived from isoprene, butadiene or a mixture thereof.
 3. An oilcomposition as claimed in claim 2 wherein the linear diblock copolymeris at least one diblock copolymer selected from the group consisting ofhydrogenated styrene/butadiene diblock copolymers and hydrogenatedstyrene/isoprene diblock copolymers.
 4. An oil composition as claimed inclaim 2 wherein the diblock copolymer has a Shear Stability Index valueof from 2 to 50% (30 cycles) and the polydiene block of the diblockcopolymer comprises from 40 to 90 mass % derived from isoprene and from10 to 60 mass % derived from butadiene.
 5. An oil composition as claimedin claim 3 wherein the diblock copolymer has a Shear Stability Indexvalue of from 2 to 50% (30 cycles) and the polydiene block of thediblock copolymer comprises from 40 to 90 mass % derived from isopreneand from 10 to 60 mass % derived from butadiene.
 6. An oil compositionas claimed in claim 1 wherein the diblock copolymer has a ShearStability Index value of from 5 to 25% (30 cycles).
 7. An oilcomposition as claimed in claim 1 having a sulphated ash concentrationof not greater than 1.0 mass %.
 8. An oil composition as claimed inclaim 1 having a sulphur concentration, expressed as atoms of sulphur,of not greater than 0.3 mass %.
 9. An oil composition as claimed inclaim 8 having a sulphur concentration, expressed as atoms of sulphur,of not greater than 0.2, mass %.
 10. An oil composition as claimed inclaim 1 wherein the metal salts of organic carboxylic acids areoverbased alkaline earth metal salicylates.
 11. An oil composition asclaimed in claim 2 wherein the metal salts of organic carboxylic acidsare overbased alkaline earth metal salicylates.
 12. An oil compositionas claimed in claim 3 wherein the metal salts of organic carboxylicacids are overbased alkaline earth metal salicylates.
 13. An oilcomposition as claimed in claim 4 wherein the metal salts of organiccarboxylic acids are overbased alkaline earth metal salicylates.
 14. Anoil composition as claimed in claim 1 further including one or moreadditives, other than (B) and (C), selected from dispersants,detergents, antioxidants, antiwear agents, friction modifiers, corrosioninhibitors, pour point depressants, demulsifiers and anti-foamingagents.
 15. An oil composition as claimed in claim 2 further includingone or more additives, other than (B) and (C), selected fromdispersants, detergents, antioxidants, antiwear agents, frictionmodifiers, corrosion inhibitors, pour point depressants, demulsifiersand anti-foaming agents.
 16. An oil composition as claimed in claim 3further including one or more additives, other than (B) and (C),selected from dispersants, detergents, antioxidants, antiwear agents,friction modifiers, corrosion inhibitors, pour point depressants,demulsifiers and anti-foaming agents.
 17. An oil composition as claimedin claim 4 further including one or more additives, other than (B) and(C), selected from dispersants, detergents, antioxidants, antiwearagents, friction modifiers, corrosion inhibitors, pour pointdepressants, demulsifiers and anti-foaming agents.
 18. A method oflubricating a compression-ignited or spark-ignited internal combustionengine which comprises supplying, to the engine a lubricating oilcomposition as claimed in claim
 1. 19. A method of lubricating acompression-ignited or spark-ignited internal combustion engine whichcomprises supplying to the engine a lubricating oil composition asclaimed in claim
 2. 20. A method of lubricating a compression-ignited orspark-ignited internal combustion engine which comprises supplying tothe engine a lubricating oil composition as claimed in claim 3.